1. Field of the Invention
This invention relates to an image-forming material used for an image-forming apparatus employing an electrophotographic system or thermal transfer system, a process for preparation of the material, and an image-receiving medium formed by the material. More specifically, the present invention pertains to an image-forming material which permits the repetition of image formation and image removal by using an apparatus for removing the image-forming material maintained on a base material or an image-forming apparatus equipped with a removal apparatus; a preparation process thereof and an image-receiving medium formed by the material.
2. Description of the Related Art
The awareness of the importance of protecting forest resources has grown recently with recognition of global environmental problems and the reduced use of wood resources as the raw material for manufacturing paper. One of the measures being promoted to reduce the amount of wood sources used is the recycling of used paper rather than disposing of it as ordinary garbage. The recycling of waste paper is an important method for recovering resources, but it involves a number of problems in the process from waste paper to recycled. The collection of waste paper, for example, is accompanied by problems such as the unwanted leakage of information from confidential documents or data particularly at business enterprises, the labor involved in collecting or transporting waste paper classified by type, the site where collected waste paper is accumulated, and how to manage such a site. Moreover, in the recycling of waste paper, waste paper pulping shortens pulp fibers, thereby deteriorating the quality of the recycled paper or it becomes necessary to add an apparatus to deink image portions. Furthermore, paper manufacturing equipment itself is so large, complicated, and expensive that it is not possible to deal with the recycling of waste paper individually and it becomes inevitable to turn to specialized enterprises. If such collection classified by paper type, transport, accumulation, and the operation of huge equipment are not done efficiently, the recycling of waste paper consumes much energy (leading to an increase in the amount of CO.sub.2 emission), which may accelerate the greenhouse effects caused by increased amounts of CO.sub.2, which has become a global environmental problem.
In order to solve such problems, a process to erase images from paper after use, followed by recycling, is disclosed. There are generally two methods for erasing images. One is to reduce the adhesion between an image-forming material and a base material (paper) by using a releasing liquid in which water or a solvent and a surfactant have been mixed, and apply heat or pressure, thereby wet-releasing the image-forming material from the base material. The other method is to release the image-forming material by applying an external force such as heat, pressure, or mechanical force without using water or a solvent, or to dry-release the image-forming material from the base material by applying heat, pressure, or mechanical force after forming an image under reduced adhesion in advance. The conventional process will hereinafter be described using examples.
Examples of the process using a releasing liquid composed of water and a surfactant include those disclosed in Japanese Patent Applications Laid-Open (JP-A) Nos. 6-250569, 6-208318, and 6-250570, wherein heat is applied to an image-receiving medium with an aqueous solution of a surfactant being retained on the medium, ink on the image-receiving medium is thermally fused, and ink is peeled away using a releasing means. In the above methods, however, the wettability between the image-retaining medium and the aqueous solution is important and the penetration of the aqueous solution into the boundary between the thermally fused ink and the image-retaining medium becomes necessary. When paper has solid-printed images on both sides, the aqueous solution does not penetrate into the boundary because it is repelled on the surface of the image-retaining medium, preventing the improving of releasability between the image-forming material and the image-retaining medium. The same can be applied to a case in which an image is released from an OHP transparency. When regeneration is repeated, toner which remains behind due to not having been removed accumulates on the image-retaining medium, which deteriorates the quality of the base material (paper). In addition, it takes many calories to dry paper wet by an aqueous solution. The above method is therefore accompanied by such problems as increased energy consumption, which increases operating costs. In a color image, as opposed to a monotone image, a larger amount of toner is used over the entire image-retaining medium, preventing the surfactant from penetrating the image-retaining medium. As a result, the surfactant, which fails to effect the release of toner and prevents the image-retaining medium from being recycled. When a color image is formed again on the image-retaining medium on which toner remains, it presumably appears as a change in the reproduction of shades.
Disclosed in JP-A Nos. 1-101576 and 1-101577 is a process in which an image-receiving medium is coated with or immersed in a soluble solvent to dissolve and remove toner resin. Disclosed in JP-A No. 4-300395 is a process in which a solvent is adhered to the image-receiving medium by immersion, spraying, or coating to dissolve the toner and the toner thus dissolved is removed by washing, suction, or adsorption, whereby the image-receiving medium is recycled. With this process, the image-forming material can be removed from the image-receiving medium but is accompanied by drawbacks such as the adverse influence of organic solvent use on the safety and environment, the requirement of much energy to dry the solvent, and the curling of paper after drying. In addition, the above process is accompanied by the problem that toner dissolved in a solvent adheres again to the image-receiving medium, preventing the image-retaining medium from maintaining sufficient quality after recycling. In any case, much energy is required to dry the releasing agent used for removing or erasing the image-forming material using a wet system. Furthermore, additives contained in the releasing agent such as surfactant are, when used repeatedly, accumulated in the image-retaining medium and may exert adverse effects on repeated image formation.
Proposed in JP-A Nos. 1-297294 and 4-67043 is a process which comprises applying a silicone sealing material or the like thinly to coat paper, drying the resulting paper to obtain paper (erasable paper) having a surface imparted with releasability, printing on the resulting paper, covering the printing with a hot-fusing material (cleaning material) under a hot-fusing condition for cleaning, cooling the paper, and then removing characters or images, printed together with the hot-fusing material, from the paper. This process is accompanied by drawbacks such as, due to insufficient adhesion between the image-forming material and the releasing agent, the releasing agent transfers from the image-receiving medium to another medium, such as a transfer roller, thereby adversely affecting subsequent image formation, or the transfer of the releasing agent changes the releasability of the image-receiving medium, thereby preventing repeated use. In general, although, with an image-receiving medium having a surface imparted with releasability, it is easy to remove the image-forming material from the base material, it involves the problem of releasing treatment deteriorating the fixability to the base material or transport property of the base material.
Disclosed in JP-A No. 6-219068 is a process in which thermal-transfer recording paper is coated or impregnated with a thermally modified material, for example, a fluorine containing acrylate material, which deteriorates in adhesion with an image-forming material when heated, whereby a recording medium which can be recycled is prepared. This process also involves drawbacks essentially similar to those of the above-described process in which the image-receiving medium has a surface imparted with releasability. In order to ensure the transport property of the recording medium, it is necessary to secure a release-treatment-free portion by sealing both edges of the receiving medium in advance.
In the above-described process for forming a releasable material on the image-receiving medium, the releasing material is formed on the medium by dissolving the releasable material in an organic solvent or the like, and then coating or impregnating the base material with the resulting solution. In other words, the releasable material is formed over the entire receiving medium, which brings about problems in the travel property or transport property of the receiving medium within the image-forming apparatus. Moreover, the above process involves problems in the quality of writing and correction because the releasable material is present even in the image-free portion. Furthermore, the releasing material is generally expensive. A method of coating or impregnating a base material with the releasable material requires a large amount of releasing material and, in addition, the releasing material has an uneconomical aspect which leads to a rise in cost.
In addition, a conventionally proposed process incorporates a releasing agent in an image-forming material in order to prevent offset in fixation by a heated roller. JP-A Nos. 58-215659 and 60-217366, for example, disclose a process in which a wax such as low-molecular-weight polyolefin is added as a releasing agent to an image-forming material. In the above official gazettes, the releasing agent is used to prevent offset, and the amount of releasing agent used is from 0.1 to 20 wt %. Generally, the amount of releasing agent is up to 5 wt % for the above purpose. If the amount exceeds the above range, marked deterioration can be expected to appear in the manufacturability of an image-forming material and powder fluidity because of the existence of the wax on the image-forming material, the image-forming material cannot be uniformly electrically charged and a defective image is formed. Moreover, such an amount may contaminate the carriers or photoreceptor.
A binding resin containing a releasable material is prepared, for example, by kneading, pulverization, and dispersion. During the pulverization step, pulverization occurs at the interface between the binding resin and the releasing agent which have been kneaded so that the image-forming forming material contains much of the releasing agent on its surface. Alternatively, there is a process comprising dispersion of an oil phase containing an image-forming material in an aqueous medium and then granulating the dispersion as, for example, the suspension polymerization process described in Japanese Patent Application Publication (JP-B) No. 36-10231 and the process described in JP-B No. 61-28688. In the suspension polymerization process, an image-forming material having a desired particle size is obtained by dissolving or dispersing raw materials such as a polymerizable monomer, colorant, and releasing agent to prepare a monomer composition and, while carrying out polymerization, using a proper stirring material to disperse the monomer composition in an aqueous phase containing a dispersion stabilizer.
Disclosed in JP-B No. 61-28688 is a process in which an image-forming material is dissolved or dispersed in an organic solvent which is almost insoluble in water, the resulting oil phase is dispersed in an aqueous phase containing a dispersion stabilizer, and then image-forming particles are formed by removing the solvent from the dispersion. Alternatively, it is also possible to prepare an image-forming material by adding a new monomer to an oil phase, which has been subjected to dispersion stabilization, causing a polymerization reaction at the interface of the oil phase, and then encapsulating the polymer. The formation of image-forming particles through a polymerization process such as suspension polymerization requires a purification step to remove the monomer from the polymer composition by solvent extraction or the like, because the polymerization reaction cannot be allowed to proceed to completion, and a problem remains about the safety of such materials. Solvent extraction, however, is accompanied by the problem that the releasing agent and other additives necessary for the image-forming material are extracted together with the monomer.